(1) Field of the Invention
This invention relates to quick connecting fasteners and more particularly to an internally threaded fastener which may be connected to an externally threaded member by axially thrusting it thereon and thereafter tightening it by rotation.
(2) Description of Related Art
The need for fasteners such as an internally threaded nut which may be quickly attached to an externally threaded member such as a bolt, screw or stud, without the time consuming need to rotate the nut a great number of revolutions to secure it to the member is well documented. For example, Howe U.S. Pat. No. 3,695,139 and Fullerton U.S. Pat. No. 4,378,187 disclose fasteners of the quick connecting type. The devices illustrated in these patents have internally threaded segments which separate to allow an externally threaded member to be pushed into the threads. The devices in both patents employ a frusto-conical surface inside the body of the nut casing to force the segments or shells inwardly upon tightening, this surface being at a large angle relative to the axis of the nut. The large angle employed allows only the front surface of the segments to contact the conical surface. Additionally, the devices employ a second frusto-conical surface at the rear of the nut casing and corresponding conical surfaces formed on the threaded segments for spreading or separating the segments when a bolt or the like is inserted. The segments are free to float within the casing and are held together by circumferential tension springs. In these devices a conical surface is relied upon to force the threaded segments into contact with the mating fastener member. Since the conical surface is at a large angle to the axis of the nut, it can only contact a short distance along the inside surface of the segments. The segments or shells are subjected to a radially outwardly directed load resulting from a component of the fastener tension directed outwardly by the standard angled thread form. This force is unopposed at the top of the segments in both devices, thereby resulting in a bending moment upon the segments attempting to rotate the segments away from the end of the mating fastener. In the aforesaid Fullerton patent the conical angle is substantially equal to the angle of the threads and experience has shown that the nut casing tends to fail at unacceptably small loads because this structure permits the radially outward force resultant of the threads to equal the radially inward force of the conical surface on the threaded segments, thereby creating a delicate equilibrium which is easily overcome by the aforesaid bending moment. The devices in both of the aforesaid patents tend to develop a large radially outward force against the conical surface of the nut casing corresponding to bolt tension. Although this load component acts to lock the nut to the fastener, the magnitude of the load is uncontrolled and may result in a split nut casing.